1. FIELD OF THE INVENTION
This invention relates in general to a microfiche processing apparatus and in particular to a diazo film advancing module which cooperates with a basic processing module for processing diazo microfilm to make duplicates of master microfiche.
2. DESCRIPTION OF THE PRIOR ART
One form of microfilm is microfiche which is generally known as a group of related images arranged on a card-like transparent sheet of film. Typically, these sheets measure 105 mm by 148 mm and are unmounted. The wide-spread use of microfiche has lead to a demand for a means of duplicating the microfiche. However, the use of three major types of duplicating film, silver film, diazo film and vesicular film, requires the utilization of three different developing processes with their associated developing apparatus.
The diazo microfilm generally has a transparent polyester base coated with a diazonium salt. When the film is exposed to a light source through a master microfiche, the salt decomposes in those areas corresponding to the transparent areas of the master microfiche. The film is then passed through a heated ammonia vapor atmosphere wherein the ammonia couples with the diazonium salt to form an opaque image corresponding to the image of the master microfiche. Therefore, the diazo film duplicate is a positive of the master microfiche.
A major problem in the diazo film developing process is the escape of the ammonia vapor from the developing chamber. Generally, the ammonia vapor is supplied to the developing chamber under pressure so that there is a tendency for the vapor to leak past the seals at the entrance and exit of the chamber thereby causing an objectionable odor in the vicinity of the film processing machine. U.S. Pat. No. 3,653,242, issued Apr. 4, 1972 to N. P. Schleich and entitled "Apparatus For Treating A Continuous Body Under Pressure", discloses an apparatus for developing a continuous strip of diazo microfilm in a sealed chamber with the entrance and exist sealed by a pressure limiting capsule. Each capsule is comprised of two cellular pressure isolation zones, each zone formed of spaced thin flexible resilient diaphragms having a longitudinal slit centrally located. Any permeation of gas from the developing chamber into the first cellular zone is minimized by close contact between the film and a first diaphragm. As a result of the slow permeation, the partial pressure of ammonia gas is less in the first zone than in the developing chamber. A second diaphragm will minimize permeation from the first zone to the second zone which is defined by the second and a third diaphragm. The diaphragm slits may be shaped to accommodate thicker films to minimize binding. Therefore, this apparatus is limited in that the diaphragms must be changed when a different thickness of film is to be processed and the pressure limiting capsule seal is not effective where film segments are to be processed since the ammonia vapor is free to leak through the slits between the film segments.
U.S. Pat. No. 3,726,590, issued Apr. 10, 1973 to J. L. Kistner et al. and entitled "Fiche-To-Fiche Copier", discloses a fiche-to-fiche copier for developing diazo film microfiche. A movable platen is driven into sealed engagement with a fixed platen to define a developer chamber into which anhydrous ammonia gas is injected and then exhausted through a water trap. Although this apparatus eliminates the presence of ammonia vapor when the microfiche enters and exits the developer chamber, a small amount of vapor is retained and released when the chamber is opened and the mechanism for operating the movable platen is more complicated and costly than a fixed developing chamber.